1. Field of the Invention
The present invention relates generally to systems for mounting semiconductor dies on conductor substrates, and more particularly to a system which provides for detachably mounting such semiconductor dies without soldering by interposing a resilient anisotropic conductor pad between the semiconductor die and the conductor substrate.
Integrated circuits are typically fabricated on relatively large silicon wafers which are then divided into a plurality of individual circuits, referred to as dies or chips. The individual dies may then be packaged in a variety of ways, including the familiar dual-in-line package, referred to as the DIP, where the die is encapsulated in plastic or ceramic. The individual DIPs may then be mounted and interconnected on printed circuit boards in order to build up the desired circuitry. Although workable, the use of discrete packages, such as DIPs, can result in unacceptable signal propagation delay time between the separated integrated circuits.
An approach which has been developed in order to reduce such signal propagation delay time involves mounting a plurality of discrete dies in a common enclosure on a single conductor substrate, typically a multilayer ceramic substrate. The dies are usually soldered directly to the conductor substrate and may be spaced together very closely in order to reduce the propagation delay time. The use of a common enclosure avoids the necessity of individually packaging the chips for protection.
The use of such multichip modules, however, suffers from a number of problems. It is desirable to have the module as small as possible in order to reduce the signal propagation delay as much as possible. The small module size makes it very difficult to locate and attach the individual dies. Moreover, the large number of dies in a single module greatly increases the likelihood of failure of the module since the chance of at least one die failing is greatly increased. Since the modules must be tested after assembly, the failure of a single die necessitates either discarding the entire module, which can be prohibitively expensive, or detaching and replacing the die or dies which have failed. Detaching the die can be very difficult since in most cases it will have been soldered to the conductor substrate. The problem is exacerbated if, as is frequently the case, the die has also been soldered to a heat sink to enhance heat dissipation.
For the above reasons, it would be desirable to provide alternate systems for the high density mounting of a plurality of semiconductor dies on a single conductor substrate. It would be particularly desirable to provide such systems which allow for detachably mounting the dies on the substrate without solder so that the dies may be easily removed from the substrate in the event of failure. The system should also provide for adequate heat dissipation without the need to solder or otherwise attach the dies to a heat sink, and should additionally provide for a minimum signal propagation delay time between the dies and the conductor substrate. Also, the electrical connections between the dies and the substrate should have a low resistance, and allow for differential thermal expansion between the dies and the substrate which is a particular problem with larger semiconductor dies.
2. Description of the Relevant Art
Modules for mounting a plurality of semiconductor dies on a common conductor substrate are described in IBM Technical Disclosure Bulletin Vol. 13, page 58; Vol. 19, pages 1270-1272; and Vol. 20, pages 3919-3920.
IBM Technical Disclosure Bulletin Vol. 25, pages 1801-1802, discloses an elastomeric layer having widely spaced, discrete spring elements embedded therein. The elastomeric layer is interposed between a chip carrier and a pin carrier to provide for electrical connection.
Elastomeric, anisotropic conductors are described in U.S. Pat. Nos. 4,003,621; 3,982,320, and 3,862,790. None of these patents suggests the use of such conductors for directly mounting a semiconductor die on a conductor substrate.
Co-pending applications Ser. No. 604,783, now U.S. Pat. No. 4,667,219 and Ser. No. 605,018, now U.S. Pat. No. 4,667,220 assigned to the assignee of the present application, disclose the use of soldered, flexible connectors mounted in a connector board for surface mounting of semiconductor dies.